There are various known corrugated plate manufacturing apparatuses, which form a corrugated metal plate product that has a corrugated pattern including alternating ridges and furrows through a press forming process. For example, JP2010-264495A discloses one such a manufacturing apparatus. The manufacturing apparatus of JP2010-264495A includes an upper die and a lower die, which are opposed to each other in a top-to-bottom direction. The upper die includes a plurality of press punches, which are stacked one after another in a direction perpendicular to the top-to-bottom direction. The press punches of the upper die are lowered to abut against a processing surface of a block member of the lower die, so that a material of a metal plate product is plastically deformed by a predetermined pressing force applied from the press punches to form the corrugated pattern. At this time, the press punches of the upper die are sequentially lowered toward the lower die at different time points, which are different from each other by a predetermined time difference, so that the corrugated pattern, which includes the alternating ridges and furrows, is formed in the material of the metal plate product.
The corrugated plate manufacturing apparatus of JP2010-264495A forms an inner fin as the corrugated metal plate product. The inner fin is placed in an inside of a tube, which conducts refrigerant and forms a part of a heat exchanger of, for example, a vehicle (e.g., an automobile). Two types of inner fins are exemplified in FIGS. 17 and 18, respectively. In FIGS. 17 and 18, multiple inner fins 90 are joined together by connecting portions 901. The joined multiple inner fins 90 are separated from each other and are placed in the tubes, respectively.
A press forming method of the inner fin is disclosed in, for example, JP2010-264495A. In one example of the press forming method, as shown in FIG. 19, cuttings are formed at predetermined pitches in a rolled metal plate material 92, and the metal plate material 92 is sequentially pulled and pressed to form the corrugated pattern on the metal plate material 92. That is, the metal plate material 92 shown in FIG. 19 is a material of the inner fin 90. As shown in FIG. 20, an upper die 942, which is opposed to a lower die 941, includes a slider 944 that drives press punches 942a of the upper die 942 downward. In the press forming process, the slider 944 is slid in the horizontal direction, as indicated by an arrow AR1.
A plurality of cam surfaces 944a is integrally formed in the slider 944. A location of each of the cam surfaces 944a in a sliding direction (see the arrow AR1) is different from a location of an adjacent one(s) of the cam surfaces 944a. Thereby, in the press forming process of the inner fin, the forming timing of each ridge or furrow formed in the inner fin upon lowering of the corresponding press punch 942a is shifted from the forming timing of the adjacent ridge or furrow formed in the inner fin upon lowering of the corresponding adjacent press punch 942a. Thereby, the corrugated pattern, which includes alternating ridges and furrows, can be formed in the metal plate material 92 without rupturing the metal plate material 92. Here, although the lower die 941 is formed integrally in the corrugated plate manufacturing apparatus shown in FIG. 20, there has been also proposed another type of corrugated plate manufacturing apparatus, in which the lower die 941 includes a plurality of press punches 941a like the press punches 942a of the upper die 942, as shown in FIG. 21.
Lately, in order to improve the performance of the heat exchanger of the vehicle, a fin pitch Pf (e.g., a ridge-to-ridge pitch or a furrow-to-furrow pitch shown in FIGS. 17 and 18) of the corrugated pattern of the inner fin 90 is reduced, and the number of the ridges Nf (see FIGS. 17 and 18) of the inner fin 90 is increased. As shown in FIGS. 22 to 24, which indicate the structure of the corrugated plate manufacturing apparatus similar to the corrugated plate manufacturing apparatus shown in FIG. 21, the inner fin 90 is formed by the press punches 942a, which are stacked one after another in a stacking direction in the upper die 942, and the press punches 941a, which are stacked one after another in a stacking direction in the lower die 941. A thickness of each of the press punches 941a, 942a, i.e., a width THp of each of the press punches 941a, 942a measured in the stacking direction is determined according to the fin pitch Pf. Therefore, when the fin pitch Pf is reduced, the thickness THp of the respective press punches 941a, 942a shown in FIGS. 22 to 24 is reduced.
FIG. 22 shows a front view of the corrugated plate manufacturing apparatus. FIG. 23 is a view taken in a direction of an arrow XXIII in FIG. 22. FIG. 24 is a view taken in a direction of an arrow XXIV in FIG. 22. In the corrugated plate manufacturing apparatus shown in FIGS. 22 to 24, the slider 944 of the upper die 942 and a slider 945 of the lower die 941 are formed together as an integral member. The slider 945 drives the press punches 941a of the lower die 941 toward the upper die 942. When the sliders 944, 945 are slid in the direction of the arrow AR1, a cam surface 942b of each corresponding one of the press punches 942a of the upper die 942 is pressed downward by a corresponding one of the cam surfaces 944a of the corresponding slider 944. Thereby, the press punches 942a of the upper die 942 are sequentially pressed downward toward the lower die 941. At the same time, a cam surface 941b of each corresponding one of the press punches 941a of the lower die 941 is pressed upward by a corresponding one of the cam surfaces 945a of the corresponding slider 945. Thereby, the press punches 941a of the lower die 941 are sequentially pressed upward toward the upper die 942.
As discussed above, when the thickness THp of the respective press punches 941a, 942a is reduced, a pressure receiving surface area of the respective sliding portions, such as the cam surfaces 941b, 942b, 944a, 945a, which receive an offset load, is reduced. In such a case, a contact pressure of the sliding portion(s) is increased at, for example, portions X1, X2, X3 shown in FIG. 25, so that galling and wearing are promoted at the sliding portion(s). In addition, when a cam contact force Fc, which is generated at the respective cam surfaces 941b, 942b (see FIG. 22), is deviated from a center of a press forming load Fp, which plastically deforms the material of the inner fin 90 in a manner shown in FIGS. 22 and 25, the galling and the wearing discussed above are further promoted. The promotion of the galling and the wearing causes a reduction in the lifetime of the upper die 942 and/or the lower die 941.
FIG. 25 is an enlarged partial view showing the lower die 941 of FIG. 22. Although FIG. 25 indicates a stripper 946 of the lower die 941, which guides movement of the respective press punches 941a of the lower die 941 in the top-to-bottom direction, the stripper 946 is not shown in FIG. 22 for the sake of simplicity. Furthermore, in FIG. 25, a dot-dot-dash line Lx indicates the press punch 941a, which is tilted by the press forming load Fp and the cam contact force Fc.
The inventors of the present application have improved the corrugated plate manufacturing apparatus shown in FIGS. 22 to 24 and have proposed a first corrugated plate manufacturing apparatus shown in FIGS. 26 and 27 and a second corrugated plate manufacturing apparatus shown in FIGS. 28 and 29. FIG. 26 is a front view of the first corrugated plate manufacturing apparatus. FIG. 27 is a view taken in a direction of an arrow XXVII in FIG. 26. Furthermore, FIG. 28 is a front view of the second corrugated plate manufacturing apparatus. FIG. 29 is a view taken in a direction of an arrow XXIX in FIG. 28.
As shown in FIGS. 26 and 27, in the first corrugated plate manufacturing apparatus, two cam surfaces 941b, which are arranged one after another in a sliding direction DR3 parallel to the direction of the arrow AR1 (see FIG. 22), are formed at two locations, respectively, in each of the press punches 941a in the lower die 941. Also, two cam surfaces 942b, which are arranged one after another in the sliding direction DR3, are formed at two locations, respectively, in each of the press punches 942a in the upper die 942. Two cam surfaces 944a, which are arranged one after another in the sliding direction DR3, are formed at two locations, respectively, in the slider 944 of the upper die 942 to correspond with the two cam surfaces 942b of the corresponding press punch 942a. Also, two cam surfaces 945a, which are arranged one after another in the sliding direction DR3, are formed at two locations, respectively, in the slider 945 of the lower die 941 to correspond with the two cam surfaces 941b of the corresponding press punch 941a. 
Furthermore, in the second corrugated plate manufacturing apparatus shown in FIGS. 28 and 29, three cam surfaces 941b, which are arranged one after another in the sliding direction DR3, are formed at three locations, respectively, in each of the press punches 941a in the lower die 941. Also, three cam surfaces 942b, which are arranged one after another in the sliding direction DR3, are formed at three locations, respectively, in each of the press punches 942a in the upper die 942. The second corrugate plate manufacturing apparatus shown in FIGS. 28 and 29 differs from the first corrugated plate manufacturing apparatus shown in FIGS. 26 and 27 with respect to the number of the cam surfaces 941b of each press punch 941a and the number of the cam surfaces 942b of each press punch 942a. 
As in the cases of the first corrugated plate manufacturing apparatus and the second corrugated plate manufacturing apparatus, when each press punch 941a, 942a receives the load from the corresponding slider 944, 945 at the multiple cam surfaces 941b, 942b of the press punch 941a, 942a, a positional deviation of a resultant force of the cam contact forces Fc, which are generated at the cam surfaces 941b, 942b of each press punch 941a, 942a, relative to the center of the press forming load Fp is reduced. Therefore, an increase in the load generated by the galling, which is induced by the positional deviation between the resultant force of the cam contact forces Fc and the center of the press forming load Fp, can be limited, and thereby the contact pressure can be reduced.
However, as shown in FIGS. 26 to 29, in each of the first corrugated plate manufacturing apparatus and the second corrugated plate manufacturing apparatus, in order to shift the forming timing of each ridge or furrow in the inner fin 90 from the forming timing of the adjacent ridge or furrow in the inner fin 90, an interval between the adjacent cam surfaces 941b, 942b formed at the two or three locations, respectively, in the respective press punches 941a, 942a is increased. Therefore, a size W2, W3 of each press punch 941a, 942a in the sliding direction DR3 is substantially increased.
In addition, moment Mp, which acts to tilt the press punch 941a, 942a relative to the pressing direction that is the top-to-bottom direction, may be generated due to the presence of unequalness of the cam contact forces Fc. The moment Mp is increased when the interval between the two or three locations, at each of which a corresponding one of the cam contacts forces Fc is applied, in the sliding direction DR3 is increased. This moment Mp may become a factor that reduces the lifetime of the press punches 941a, 942a. That is, when the interval in the sliding direction DR3 between the adjacent cam surfaces 941b, 942b of the press punch 941a, 942a pressed by the corresponding slider 944, 945 is increased, the lifetime of the press punch 941a, 942a is possibly reduced. Furthermore, when the interval between the adjacent cam surfaces 941b, 942b in the sliding direction DR3 is large, a slight deviation in the timing for pressing the cam surfaces 941b, 942b of the one press punch 941a, 942a by the one slider 944, 945 causes generation of the large moment Mp.